Similarly, yeast 2-hybrid (Y2H) and mammalian 2-hybrid (M2H) experiments (Imbert et al., 2008; Pan et al., 2008; Prentice et al., 2004; von Brunn et al., 2007) , pull down assays or co-purifications (e.g. (Brockway et al., 2003; Imbert et al., 2008; Subissi et al., 2014b; Sutton et al., 2004; von Brunn et al., 2007) ) and co-crystallization studies (e.g. (Decroly et al., 2011; Ma et al., 2015; Zhai et al., 2005) ) have implicated several additional CoV nsps and the nucleocapsid (N) protein as potential viral cofactors of the RNA polymerase.